This invention relates generally to an improved ultrasonic surgical apparatus for enhancing tissue fragmentation.
Ultrasonic surgical apparatus and aspirators have gained widespread acceptance in the microsurgical field. They have been used successfully for the fragmentation and removal of body tissue. Essentially, an apparatus of this type includes an ultrasonic transducer housed in a handpiece. Such ultrasonic transducers are operable for converting electrical energy supplied thereto into high velocity vibrational movements. The transducer generated ultrasonic vibrations are transmitted to a surgical operative tip that is coupled thereto.
In cataract surgery, for example, the operative tip is insertable through a small incision formed in the eye and is manipulated so as to actually contact the cataractous lens. Ultrasonic vibrations cause the lens to fragment. The tissue fragments and other body fluids including irrigation fluid are aspirated from the surgical site by an aspiration system that includes an aspiration passage extending through the operative tip. The aspiration is established by an external vacuum pump located on an external control device. The fragmentation of the lens is the result of cutting action introduced by the vibrating tip and the disruptive cavitation developed by the intense ultrasonic field adjacent the operative tip. Known prior art ultrasonic devices, such as described in U.S. Pat. No. 4,750,902, tend to produce high cutting displacement at the operative tip. However, uncontrolled cavitation especially in ophthalmic surgical procedures, such as cataract surgery, can lead to a variety of problems including inefficient and prolonged fragmentation. Efficient fragmentation is, however, desirable because it reduces the size of the tissue particles entering the aspiration passageway. Since these aspiration passageways are relatively small (e.g., 2 mm) it is important to avoid occlusion or blockage thereof. Occlusion also has other drawbacks since it tends to create significant negative pressure in the aspiration system. Moreover, uncontrolled cavitation creates a degree of turbulence motion in the eye which draws fragmented tissue particles longitudinally away from the tip opening. As a consequence, the efficiency of the fragmentation and aspiration are diminished. Furthermore, the swirling bubble action created by cavitation has a tendency to obscure or cloud the visibility around the operative site so as to hinder the physician during the operation. Moreover, cavitation can be produced by tool portions such as the tip nut or other sections of the ultrasonic horn and can lead to an unnecessary waste of power.
Ultrasonic surgical devices of the kind discussed above are usually operated at relatively high mechanical displacement. High mechanical displacement generates heat any time a frictional force has to be overcome. Most of the frictional losses are generated within the threads used to couple different sections of the handpiece. It is common practice to use threads for coupling the tip with the horn and to use a threaded bolt for compressing the piezoelectric elements between two metal cylinders in a sandwich-type configuration. If those threads are placed in a high vibrational displacement area then we should expect temperature increases especially if the fluid flow stops due to an occlusion. Besides several ultrasonic surgical aspirators utilize low frequency (i.e., below 40 KHz) which only enhances cavitation and thus eye turbulence.
However, in certain instances it is desired to maximize the vibrational displacement of the operative tip. In such situations it is desirable for reasons including safety to minimize the electrical power applied to the handpiece.